1. Field of the Invention
The present invention relates to ironing dies, and in particular to ironing dies suitable for press forming processes including ironing.
2. Description of the Related Art
Press forming including ironing has so far been widely used for producing numerous goods and have been contributing a great deal to all the human beings with respect to the improvement of living conditions and rise of living level.
In such press forming including ironing as mentioned above, many kinds of forming and ironing dies are selected and used to be suitable for each of various products.
The feature of press forming including ironing is characterized by attaching an ironing die firmly to a work material, and thereby exerting a very strong force on a work material in forming, and deforming the work plastically to produce the products of required geometry.
It is therefore difficult sometimes to take the formed product from the ironing die because the die and the product are very close to each other in size, and thereby lower the efficiency of forming.
In particular, the work is given a required force to deform plastically during forming, and thereafter deforms elastically backward from the direction of given deformation during unloading. The elastic return of deformation is called “springback”. When the formed product becomes larger by springback, it is harder to remove the product from the die cavity. When the formed product becomes smaller, it is harder to remove the product from the punch.
As for ironing dies in press forming including ironing, it is well known that the part of the ironing dies strongly contacting to the work material is subjected to severe abrasion.
As very anti-abrasive materials are more often used for the part of ironing dies strongly contacting to the work materials, so there is no big choice in the selection of die material for ironing dies.
Besides, there is another difficulty to raise the forming limit because the rupture of lubricant film between the ironing die and the work material takes place easily in case of using conventional ironing dies.